Bring the wine to a simmer in a large pot. Add the clams, cover and return to a simmer. Lift the clams out of the pot as they open, setting them on a sided baking sheet. When all are cooked, strain the cooking liquid into a bowl and reserve.
When cool, remove the meat from the shells and set in a second bowl. (If desired, you could leave some of the meat in the half shell to decorate the top of the chowder as shown in the photo). Strain the liquid on the baking sheet into the reserved cooking liquid.
Melt the butter in a second pot set over medium heat. Add onion, celery and garlic and cook until tender, about 5 minutes. Mix in the flour and cook 2 minutes more. While mixing steadily, slowly stir in the reserved clam cooking liquid. Now add the clam nectar, tarragon, bay leaf, potatoes and corn. Bring to a boil, and then reduce the heat to a gentle simmer. Cook until the potatoes are just tender, about 10 minutes. Mix in the reserved clam meat and cream or milk. Simmer a few minutes more, and then season with salt and pepper. Ladle chowder into bowls, sprinkle with chopped parsley, and serve.
Note: Clam nectar is available in our canned seafood aisle.